Az1 is the Azimuth or Bearing going toward the Beginning of the Curve (PC) This data can be taken off of plans or if you have coordinates on this center line then you can inverse between 2 of them to find it.

Az2 the same inplies,if you do not have the data or coordinates then you can solve the Azimuth of the new tangent leaving the Curve at the (PT) End of curve or point of Tangent from the Central Angle or also called the Delta angle.. I will give you a lesson in Coordinate geometry it contains how to solve curve data..do not let the word Tangent confuse you. tangent means straight line,but the term is also use in curve data. As as the dist between the PC to the PI then to the PT ,this is also apart of the curve it also implies a Trigonometry Function. This program in the Total Station is solving where points are in relation to the Arc line or center line of the curve. See attached file

Also I am assuming that this question is on Arc reference line.

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Thank you, this is first I here of this. I have only used a few on board programs for downloads, most came with the Total Station. I have and prefer to use Data Collectors and mainly used HP calculators before them even though I had the on board programs I have and do use programs in my calculator, I had more programs than the Total Station had and I still do. I still prefer to use a Data Collector when collecting large files with many points. But thanks ,I will look for this,to learn more.